The EATCS Award 2008

Laudatio for Professor Leslie Valiant

The EATCS Award is awarded annually to honor scientists for extensive and widely recognised contributions to theoretical computer science over a life long scientific career. The 2008 award committee and the council of EATCS have decided in unanimous votes to honor

Professor Leslie Valiant

with the EATCS Award 2008, in recognition of his deep and influential achievements and his lasting merits to our field.

Leslie Valiant is world-renowned for his revolutionary, extensive and widely recognized contributions to theoretical computer science over a life long scientific career. He made seminal contributions to computational learning theory, computational complexity, parallel and distributed computation, cognitive theory and holographic algorithms. Let us briefly highlight some of these contributions.

Valiant’s “Theory of the Learnable” has literally created the area of computational learning theory, and his viewpoint was adopted by many in the artificial intelligence community as the path to understanding and designing intelligent systems. Valiant not only created this area, but also made continuous significant contributions to its development. He provided a general framework as well as concrete computational models for studying the learning process, such as the PAC model, which lead to the development of a fundamental scientific theory, with numerous applications in wide areas of computer science and other scientific disciplines.

Valiant also made numerous seminal contributions to the field of computational complexity. He introduced the class of counting problems #P, and proved that the permanent is complete for this class. Beyond their fundamental importance, these innovations have served computational complexity in unforeseen ways, for example, in unveiling the power of interactive proofs, PCPs and program checking. Valiant has contributed greatly also to the study of Boolean circuit complexity, and introduced the fundamental concept of superconcentrators, which also led to developments in other fields, such as communication, sorting networks and error correcting codes.

In the area of parallel and distributed computation, Valiant’s ingenious randomized distributed routing algorithm provides a way of avoiding congestion in sparse networks. His novel ideas and the challenges he posed for parallel computing shaped the direction of the field, and yielded the development of some of the most basic parallel algorithmic techniques currently available.

More recently, Valiant has branched into new directions. He contributed to computational neuroscience, offering a concrete mathematical model of the brain, relating its architecture to complex cognitive functions. He also developed a novel algorithmic technique based on “holographic” reductions.

Leslie Valiant’s research career has spanned computer science, mathematics, artificial intelligence and cognitive theory, and is unique in terms of the number of important research areas that he, single-handedly, created or completely transformed. His influence on the European research community of theoretical computer science is evident to anyone observing the focus shifts within this community and its progress in the last two decades.